Aircraft tire with improved bead structure

ABSTRACT

A pneumatic radial ply tire  100  for use on aircraft has a radial reinforced carcass  20  having at least one axially inner ply  2 A,  2 B,  2 C and  2 D of textile cords  21  wound around a pair of bead cores  33 . The improved bead structure  30  has a flipper  50  having an axially inner leg L I  and axially outer leg L E . The ends L I , L E  of the flippers  50  are above the bead core height B h  and below the apex A of an elastomeric strip  40  satisfying the relation B h &lt;L E &lt;0.7D and B h &lt;L I &lt;0.7D. Additionally, the tire carcass  20  has at least one axially outer ply  2 E,  2 F of textile cords  21  extending from bead  30  to bead  30  along the turn-ups  20 A,  20 B,  20 C and  20 D of the axially inner plies  2 A,  2 B,  2 C and  2 D. The plies  21  are closely spaced along the natural ply path.

This is a Divisional of application Ser. No. 09/944,819, filed Aug. 31,2001, now U.S. Pat. No. 6,648,041.

TECHNICAL FIELD

The present invention relates to a tire with radial carcassreinforcement intended to support heavy loads and inflated to relativelyhigh pressures for high speed use, in particular an airplane tire.

BACKGROUND OF THE INVENTION

The radial carcass reinforcements of such tires generally compriseseveral plies of textile cords, which are anchored in each bead to atleast one bead wire and generally have a single bead wire. Thereinforcing elements of these reinforcements are wound around said beadwire from the inside to the outside, forming turn-ups, the respectiveends of which are spaced radially from the axis of rotation of the tire.The severe conditions under which airplane tires are used are such thatthe life of the beads is short, particularly in the area of the turn-upsof the carcass reinforcement.

A substantial improvement in performance is obtained by the separatingof the plies of the carcass reinforcement into two groups. The firstgroup comprises the plies of the carcass reinforcement which are axiallytowards the inside in the region of the beads, these plies being thenwound around a bead wire in each bead from the inside to the outside ofthe tire. The second group is formed of at least one axially outer plyin the region of the beads, which ply is generally wound around the beadwire from the outside to the inside of the tire. Such arrangements areknown; for instance, in U.S. Pat. No. 4,244,414.

The life of beads formed in this manner can be improved by the presencein each bead of an additional reinforcement ply, wound around the beadwire and thus forming an axially outer leg and an axially inner leg,said reinforcement ply, also known as an inner flipper, being the plyclosest to the rubber filler, radially above the anchoring bead wire. Atire structure of this type is shown in U.S. Pat. No. 5,285,835. In U.S.Pat. No. 5,769,982, the life of the beads of airplane tires can befurther improved, particularly when they are subjected to heavyoverloads which can result in a crushing of the order of 50% and more oftheir height, by having the arrangement of the ends of the turned-upportions or turn-ups of the inner carcass plies and the ends of the legsof the inner flipper with respect to the radial position of the radiallyupper end of the rubber filler located above the anchoring bead wire andthe filler.

In accordance with that invention, an airplane tire, inflated to a highpressure, having a tread, a crown reinforcement, and a radial carcassreinforcement comprising at least two axially inner plies of textilecords wound around a bead wire in each bead from the inside to theoutside forming turn-ups and at least one axially outer ply of textilecords superimposed on the inner plies below the crown reinforcement andalong the turn-ups in said beads, said bead wire being radiallysurmounted by a filler of vulcanized rubber mix, having the shapesubstantially of a triangle, the apex of which radially furthest fromthe axis of rotation is at a distance D from a straight line parallel tosaid axis, passing through the geometrical center of the circlecircumscribed on the cross-section of the anchoring bead wire, known asthe reference line, and also comprising at least one inner flipper woundaround the bead wire to form an axially inner leg and an axially outerleg which are axially adjacent to the filler above the bead wire,characterized by the fact that the end of the axially outer leg of theinner flipper is located at a radial distance LE from the reference linesuch that LE is between 0.40 D and 0.80 D; the end of the turn-up of theinner carcass ply arranged axially furthest to the inside is located ata distance HA from the reference line such that HA is between 0.15 D and0.50 D, and by the fact that the ends respectively of the inner leg ofthe inner flipper and of the turn-ups of the inner carcass ply or plieswhich are axially furthest to the outside.

While this construction is durable, it limits the number of carcassplies that can be provided in the bead area and the extended length ofthe flipper means that the outer plies being turned down around the beadand the inner plies are spaced from the natural ply path of the tire inthe region of the flipper. This spacing, while believed desirable,results in one less ply being available in the structure and in the caseof very large aircraft the tire structure ideally may require the use ofanother ply which is effectively precluded by the use of the extendlength flipper.

It is an object of the present invention to provide a lightweightefficient tire structure having superb durability.

It is a further object of the present invention to provide an improvedbead structure wherein the use of inside turn-up plies and outsideturndown plies is optimized by the placing of the plies close to thenatural ply path.

SUMMARY OF THE INVENTION

A pneumatic tire for use on aircraft has a nominal bead diameter N_(BD),a crown reinforcement, and a radial carcass reinforcement having atleast two axially inner plies of textile cord wound around a pair ofbead cores, the bead cores having a maximum radial height Bh. Eachinside ply is wound around the bead from inside to outside formingoutside turn-ups. At least one axially outer ply of textile cordsextends from bead to bead along the turn-ups of the inner plies. Eachbead has an elastomeric filler of substantially triangular shape, theapex of the filler is located above the bead core extending to an apex Aas measured from a line YY′ parallel to the axis of the tire and passingthrough the location of the nominal bead diameter or as measured from areference line XX′ parallel to the axis of rotation and passing throughthe geometric center of the bead core.

The tire has a flipper wound around the bead core to form an axiallyinner leg and an axially outer leg, the axially inner leg is located ata radial distance Li from the reference line YY′ or XX′ and the axiallyouter leg is located a radial distance Le from the reference line YY′ orXX′. The flipper is oriented where Bh<LE<0.7D and Bh<LI<0. 7D and atleast one axially inner ply has turn-ups when the tire has two or moreaxially inner plies, at least one turn-up is radially above the apexlocation A and at least one turn-up is below the location A.

The ends of the axially outer leg of the flipper and the ends of theturn-ups of the inner plies are radially staggered.

Definitions

“Apex” means a non-reinforced elastomer positioned radially above a beadcore.

“Aspect ratio” of the tire means the ratio of its section height (SH) toits section width (SW) multiplied by 100% for expression as percentage.

“Axial” and “axially” means lines or directions that are parallel to theaxis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim.

“Belt or breaker reinforcing structure” means at least two layers ofplies of parallel cords, woven or unwoven, underlying the tread,unanchored to the bead, and having both left and right cord angles inthe range from 17° to 33° with respect to the equatorial plane of thetire.

“Bias ply tire” means a tire having a carcass with reinforcing cords inthe carcass ply extending diagonally across the tire from bead core tobead core at about a 25°–50° angle with respect to the equatorial planeof the tire. Cords run at opposite angles in alternate layers.

“Carcass” means the tire structure apart form the belt structure, tread,under tread, and sidewall rubber over the plies, but including thebeads.

“Circumferential” means lines or direction extending along the perimeterof the surface of the annular tread perpendicular to the axialdirection.

“Chafers” refers to narrow strips of material placed around the outsideof the bead to protect cord plies from the rim, distribute flexing abovethe rim, and to seal the tire.

“Chippers” means a reinforcement structure located in the bead portionof the tire.

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Flipper” means a reinforced fabric wrapped about the bead core.

“Footprint” means the contact patch are area of the tire tread with aflat surface at zero speed and under normal load and pressure.

“Innerliner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire.

“Net-to-gross ratio” means the ratio of the tire tread rubber that makescontact with the road surface while in the footprint, divided by thearea of the tread in the footprint including non-contacting portionssuch as grooves.

“Normal inflation pressure” refers to the specific design inflationpressure and load assigned by the appropriate standards organization forthe service condition for the tire.

“Ply” means a continuous layer of rubber-coated parallel cords.

“Radial” and “radially” means directions radially toward or away fromthe axis of rotation of the tire.

“Radial-ply tire” means a belted or circumferentially-restrictedpneumatic tire in which the ply cords which extend from bead to bead arelaid at cord angles between 65° and 90° with respect to the equatorialplane of the tire.

“Section height (SH)” means the radial distance from the nominal rimdiameter of the tire at its equatorial plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a partial cross-sectional view of the prior art tire bead asdescribed in U.S. Pat. No. 5,769,982.

FIGS. 2 and 3 are a partial cross-sectional views of the bead portion ofthe tire made according to the present invention.

FIG. 4 is a cross-sectional view of the tire.

FIGS. 5A, 5B and 5C, and 5D are partial cross-sections showing the tireof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, diagrammatic view in cross section of a priorart tire bead in accordance to U.S. Pat. No. 5,769,982 is shown.

The example described is that of a prior art tire 10 of standard size36×11.0 R 18 (standards of the Tire and Rim Association). The carcassreinforcement 1 is formed of five plies 1A to 1E of radial textilecords. Radial cords, as the term is used herein, are cords which formwith the circumferential direction of the tire angles which may bewithin the range of 90°+/−10°. Among these five plies, three axiallyinner plies 1A, 1B, 1C are wound in each bead 2 around a bead wire 3shown in the drawing as having a circular cross section, extending fromthe inside to the outside of the tire P in order to form turn-ups 10A,10B, 10C.

The cross section of the bead wire 3 is surmounted radially towards theoutside by a strip or filler 4 of elastomeric mix having substantiallythe shape of a triangle, the apex A of which, radially furthest from theaxis of rotation of the tire, is located at a distance D from areference line XX′. The reference line is parallel to the axis ofrotation and through the geometrical center O of the circlecircumscribed on the cross section of the bead wire 3, which circle, inthe case described, is identical with the cross section itself.

The turn-up 10A of the inner carcass ply 1A axially furthest towards theinside has its end spaced radially form the line XX′ by the amount HA,which is equal, in the case studied, to 12 mm, namely 0.33 times thedistance D, D being equal to 36 mm. As to the ends of the inner plies10B and 10C, respectively, they are located radially above the apex A ofthe filler 4 at distances HB and HC of 55 mm and 68 mm, respectively.

The same is true of the radial end of the axially inner leg of a flipper5, which can be formed of radial textile cords identical to the carcassply cords (but which may also be different), which end is located at aradial distance LI of 80 mm from the line XX′, a distance greater thanthe distances HB and HC referred to above, the three ends thus arrangedradially above the apex A being staggered between said apex and thepoint of the sidewall where the tire has a maximum axial width. As tothe radial end of the axially outer leg 5E of the inner flipper 5, it isspaced from the line XX′ by the radial distance Le equal to 0.58 D andgreater than the distance HA.

The two carcass plies 1D and 1E, herein called outer plies, cover theturn-ups 10A, 10B, 10C of the inner carcass plies 1A to 1C axially onthe outside. The plies 1D and 1E are wound around the bead wire 3 over aportion or circular arc corresponding to an angle at the center of thecircle circumscribed on the bead wire 3 equal to at most 180°, so thatthe ends of these plies 1D and 1E are situated radially below thereference line XX′.

The tire bead 2 is supplemented by a reinforcement ply 6 or outer chaferof radial textile cords, said ply permitting a better distribution ofthe pressures between the tire and its service rim, as well as assuringprotection of the carcass plies against injury upon mounting.

The axially outer end 6E of said chafer is slightly above (about 2 mm)the reference line XX′, while its axially inner end 6I is below saidline.

This prior art structure has been tested on a dynamometric flywheelunder punishing conditions for beads of this type, these conditionscorresponding to a simulation of travel on a runway (10160 kg, 4572 m,46 km/hr), followed by a take-off from 0 to 300 km/hr, the pressureconditions being such that the crushing of the tire under the load of10160 kg is 50%+/−2% of its height.

Comparison with another prior art tire of the same size comprising thesame number of carcass plies and inner and outer flipper and chafer, theinner carcass ply furthest to the inside having a turn-up end of whichis located above the apex A, and the outer leg of the inner flipperhaving its end below said apex, clearly and unexpectedly shows theimprovement, in the life of the beads, since the tires of the invention,under the above conditions, have completed on the average 35% morerunway-take-off cycles.

In contrast, the tire 100 of the present invention is illustrated in adiagrammatic view in cross-section FIGS. 2 and 3.

The example shown is that of a tire of standard size 50×20.0R22(standard of the Tire and Rim Association).

With reference to FIGS. 2 and 3, the carcass reinforcement 20 is formedof six plies 2A to 2F of radial textile cords 21. The ply cords 21 canbe nylon, rayon, or Kevlar™, or steel. Among these six plies, fouraxially inner plies 2A, 2B, 2C and 2D are wound in each bead around abead core 33 shown in the drawing having circular cross section. Thesefour plies extend from the inside to the outside of the tire in order toform turn-ups 20A, 20B, 20C and 20D. The carcass reinforcement isradially outward of the innerliner 22 of tire 100.

Outward of the bead core 33 is a strip or filler 40 of elastomericmaterial commonly referred to as an apex 40 having a substantiallytriangular shape extending to an apex location A radially furthest fromthe axis and located a distance D from a reference line XX′. As wasshown in FIG. 1 the reference line is also parallel to the axis ofrotation and through the geometric center O, of the circle circumscribedon the cross section of the bead core 33.

The turn-up 20A of the inner carcass ply 2A axially furthest toward theinside has its end spaced radially from line XX′ by the amount H_(2A),which is, for this exemplary tire size, equal to 29 mm or 0.6 times thedistance D, D being equal 48 mm.

As shown, the tire of FIG. 3 has a nominal bead diameter NBD of 22.00inches (558.8 mm). The line YY′ passing through the location of thenominal bead diameter and parallel to the tires axis of rotation whereinthe inner most ply 2A has the turn-up 20A at end H_(2A) located 2.0inches (51 mm) above the line YY′ as illustrated in FIG. 3. Forcomparative purposes with the prior art tire of FIG. 1, FIG. 2 shows allthe relationship relative to the reference line XX′. In FIG. 3 all thesecomponents are shown relative to the reference line YY′. This referenceline is parallel to and passed through the nominal bead diameter N_(BD).

As to the turn-up ends 20B, 20C and 20D of the inner plies 2B, 2C and 2Drespectively they are located at a distance H_(2B), H_(2C) and H_(2D) of85.5 mm, 17.1 mm and 106 mm above the line XX′ respectively, or asmeasured from line YY′ in FIG. 3, H_(2A), H_(2B), H_(2B) and H_(2D) arelocated 50.8 mm, 106.5 mm, 38.1 mm, and 127 mm, respectively. Thisconstruction insures the ends are all staggered having pairs of ends 20Band 20D well above the apex A location and pairs of ends 20A and 20Cwell below the apex A, each pair set 20A, 20C or 20B, 20D is preferablyspaced at least 2.0 inches (50.8 mm) apart. The lowest pair of ends islocated very close to the bead and is interposed between the bead andthe rim flange vertical surface.

As opposed to the prior art tire having three plies 1A, 1B and 1Cwherein the ends location satisfies a relationship where 10A<10C<10B thepresent invention has the ends location satisfy the relationship where20C<20A<20B<20D. As shown this creates an opportunity to have a veryefficient bead structure. The plies 2A through 2D provide a uniquecombination of ply ends 20A, 20C wherein 0.5 Bh<20C<20A<0.7D. As shownthe next ply of the wrapping inner plies is a high ply 2B or 2D. The plyends 20B and 20D satisfy the relationship where A (apex)<20B or20D>[W_(L)] the radial location of the maximum section width W_(h) whenmeasured from the nominal bead diameter. Wh is the maximum section widthof the tire 100.

A flipper 50, which can be formed of radial textile cords 51 similar tothose of plies, is located with an inner end Li slightly above theheight Bh of the bead core 33 and an outer end LE is also shown slightlyabove the bead core 33 as measured from line YY′. The ends LI, LEsatisfy a relationship wherein Bh<LI and LE<0.7D as measured from thenominal bead diameter N_(BD). To minimize the space occupied by theflipper 50 the cords 51 can be made of a diameter smaller than the plycords 21.

The carcass further has two carcass plies 2E and 2F herein called outerplies. These outer plies cover the turn-ups 20A through 20D of the innerplies 2A through 2D. The plies 2E and 2F are wound around the bead core33 over a portion of the circular arc at least past the center of beadcore 33 on the radially inner portion. The ply ends 20E and 20F are thusaxially inward of the lowest portion of the bead core 33. The ends 20Eand 20F are these effectively pinched between the bead core 33 and therim seat helping to securely anchor these outer plies 2E and 2F.

The tire bead may have an outer chipper 60 of textile cords 61 as shownwrapped around the ends 20E and 20F assuring protection of the carcassplies against injury during mounting. Preferably radially below thechipper 60 is a chafer 11 having a rubber gauge 11 in the range of 0.04inches (1.0 mm) to about 0.16 inches (4.1 mm).

Axially outward of the chafer and the plies 20E and 20F is an elongatedstrip 8 of elastomeric material extending from radially inward of thebead adjacent the chafer to a radial location at or slightly above theturn-up 20B but below the turn-up 20D. As shown, this strip 8 isinterposed between the sidewall rubber 9 and the outer ply 20F. At alocation almost equal to the radial height D of the apex location A, thestrip 8 has a maximum thickness t. In the tire size shown the maximumthickness t is 0.3 inches (7.6 mm).

The rubber properties of the various bead components are selected toprovide a cool running tire under high loads and pressures. Whenmeasured the modulus (M300) MPa, of the apex is in the ranges of 20 to25, the rubber of the plies is in the range of 14 to 18, the strip 8 isin the range of 13 to 16 and the sidewall 9 is in the range of 5 to 8.The material (M300) modulus is based on a cure rate of 80 min@135° C.The above components have the following relationship in terms of modulusapex>ply≧strip>sidewall. In the illustrated embodiment the rubberproperties of the sidewall 9 was 7.2 MPa, the apex was 20.2 MPa, theinner plies 2A through 2D were 17.0 MPa, the outer plies 2E, 2F were17.0 and 14.1 MPa, respectively, and the strip 8 was 14.1 MPa.

The resultant structure has the inner plies 2A through 2D and outerplies 2E and 2F closely spaced being separated in the area directlyabove the apex location A by a thickness of two ply layers extending adistance of over 1.0 inch (25.4 mm), preferably about 1.5 inches (37.6mm) above the apex location A, which is further reduced to a space ofone ply layer thickness or about 0.06 inches (1.5 mm) over a furtherradially outward distance of less than 1.0 inches (25.4 mm) and then theplies 2D and 2E are adjacent thereafter extending to the opposite bead30. This creates a very narrow ply path closely approximately thetheoretical optimum neutral or natural ply line. Those skilled in theart appreciate the neutral or natural ply line is the location whereinthe shear stresses along the ply line are zero. The closer the plies arepositioned along the neutral or natural path the less shear energy. Whenthe tire is severely deflected the inner plies 2A through 2D move intotension, being above the neutral or natural ply path while the outerplies 2E and 2D almost adjacent the neutral or natural ply path wereslightly compressed most of the compressive strain and shear energy isabsorbed by the strip 8. The amount of compressive shear loading isgreatly reduced when compared to the prior art tire. This means that thetire can be built with one more inner ply 2D yielding a higher strengthtire capable of more load carrying capacity based on the approximately3.0 inches (76 mm) of flipper length that can be eliminated.

The tire 100 in the example was a 50×20.0R22 tire size having a 32-plyrating, the reduction of the flipper length saved approximately 6 lb pertire. As one can readily appreciate weight saving are very importantfeature in aircraft tire design. The tire of the exemplary size was madefor the Boeing 777 aircraft.

The tire of the present invention provides an unexpected and beneficialweight reduction by reducing the flipper size to the amount needed toprevent the plies 2A–2F, particularly 2D adjacent the bead from frettingand freying due to abrasion against the bead core 3.

The flipper 50 being located well below the apex location A means thereis an opportunity to keep the inner plies and the outer plies muchcloser to the optimum natural ply path. The cords 51 of the flipper canbe made equal to or smaller in diameter than the cords 21 of the plies.The cord 51 when made of a diameter of 0.56 mm has a strength of 840denier/d, at 1.02 mm diameter the cord 51 has a strength of 1890 d/3, at1.22 mm diameter the cord 51 has 1890 d/4. In each case the textilematerial was nylon 66.

The ply cords 21 were of the size 1.22 mm in terms of diameter.

With reference to FIGS. 5A through 5D, various alternative constructionsare illustrated. In FIG. 5A, the carcass employs two axially inner plies2A, 2B and two axially outer plies 2C and 2D. In FIG. 5B, the carcasshas two axially inner plies 2A, 2B and one axially outer ply 2C. In FIG.5C, the carcass employees three axially inner plies 2A, 2B, and 2C, andtwo axially outer plies 2D and 2E. In FIG. 5D, the carcass has a threeply inner and two ply outer construction as in FIG. 5C, but with avariation in the end locations of the respective turnups. Othercombinations such as four, five and six axially inner plies incombination with two axially outer plies, are feasible. The additionalplies being employed to increase the load carrying capacity of thetires.

The rubber chafer 11, as shown in FIGS. 2 and 3, has a minimum gaugethickness Z in the range of 0.04 inches (1.0 mm) to 0.16 inches (4.1mm). The minimum gauge thickness Z when less than 0.04 inches (1.0 mm)can cause the bead base to crack resulting in a slow loss of tirepressure. When the thickness Z exceeds 0.16 inches (4.1 mm) the bead andthe plies can rock or rotate back and forth under load. This creates alarge amount of movement of the bead under overload conditions. Thedistance Z is measured under the bead from the radially innermost cord21 or 61 of a ply 2 or a chipper 60, if used.

The rubber chafer 11 has a radially inner first edge RI and a radiallyinner second edge RE. Each edge RI and RE is radially located above aline P, P being parallel to the axis of rotation and tangent to theradially innermost location of the bead core 33. Each edge is alsolocated a distance of 50% or less of the distance D as measured fromline XX′. The benefits of this particular location of the first chaferedge RI is that the tire mounting and umounting equipment is less proneto catch the edge at this location. The edge RI must be below 50% Dbecause the tensile stresses above 50% D are excessively high and couldcause a cracking of the radially inner edge RI under cyclic loading.

The second radially outer edge RE is ideally located above the line P toprevent the plys 20 E and 20 F from becoming loose in the heel regiondue to high compressive stresses and strains in this location undersevere loads. The edge RE also must be located below 50% of the distanceD to prevent the rubber between the outer plys 20 E and 20 F and thesidewall chafer interface from becoming too high in heat generationunder severe overload conditions. This is particularly true due to thehardness of the chafer 11 relative to the sidewall rubber, it beingunderstood that high shore hardness rubbers used in chafer can yieldhigh heat build ups.

As can be easily appreciated, the tire of the present invention canresult in a very high strength structure of great durability for itsotherwise light weight.

1. A pneumatic tire for use on aircrafts comprising: a nominal beaddiameter N_(BD), a tread, a crown reinforcement, and a radial carcassreinforcement comprising at least one axially inner ply of textile cordwound around a pair of bead cores, the bead cores having a radial heightB_(h), the at least one axially inner ply being wound around the beadcore in each bead from inside to the outside forming outside turn-ups,and at least one axially outer ply of textile cords extending from beadto bead along the turn-ups of the inner plies, each bead having anelastomeric filler of substantially triangular shape, the apex A of thefiller being located above the bead core extending a distance D asmeasured from a line YY′ parallel to the axis of the tire and throughthe location of the nominal bead diameter, and a flipper wound aroundthe bead core to form an axially inner leg and an axially outer leg, theaxially inner leg being located at a radial distance L_(I) from thereference line YY′, and the axially outer leg being located a radialdistance Le from the reference line YY′, wherein L_(I)>B_(H), andLE<0.7D; and a chafer, the chafer having a minimum rubber gauge Z, Zbeing in the range of 0.04 inch (1.0 mm) to 0.16 inch (4.1 mm) asmeasured from the radially innermost cord under the bead core.